Many modern medical procedures require that synthetic medical devices remain in an individual undergoing treatment. For example, coronary and peripheral procedures involve the insertion of diagnostic catheters, guide wires, guide catheters, PTCA balloon catheters (for percutaneous transluminal coronary angioplasty) and stents in blood vessels. In-dwelling sheaths (venous and arterial), intraaortic balloon pump catheters, tubes in heart lung machines, GORE-TEX surgical prosthetic conduits and in-dwelling urethral catheters are other examples. There are, however, complications which can arise from these medical procedures. For example, the insertion of synthetic materials into lumen can cause scaring and restenosis, which can result in occlusion or blockage of the lumen. Synthetic materials in the blood vessels can also cause platelet aggregation, resulting in some instances, in potentially life-threatening thrombus formation.
Nitric oxide (referred to herein as xe2x80x9cNOxe2x80x9d) inhibits the aggregation of platelets. NO also reduces smooth muscle proliferation, which is known to reduce restenosis. Consequently, NO can be used to prevent and/or treat the complications such as restenosis and thrombus formation when delivered to treatment sites inside an individual that have come in contact with synthetic medical devices. In addition, NO is anti-inflammatory, which would be of value for in-dwelling urethral or TPN catheters.
There are, however, many shortcomings associated with present methods of delivering NO to treatment sites. NO itself is too reactive to be used without some means of stabilizing the molecule until it reaches the treatment site. NO can be delivered to treatment sites in an individual by means of polymers and small molecules which release NO. However, these polymers and small molecules typically release NO rapidly. As a result, they have short shelf lives and rapidly lose their ability to deliver NO under physiological conditions. For example, the lifetime of S-nitroso-D,L-penicillamine and S-nitrosocysteine in physiological solution is no more than about an hour. As a result of the rapid rate of NO release by these compositions, it is difficult to deliver sufficient quantities of NO to a treatment site for extended periods of time or to control the amount of NO delivered.
Polymers containing groups capable of delivering NO, for example polymers containing diazeniumdiolate groups (NONOate groups), have been used to coat medical devices. However, decomposition products of NONOates under oxygenated conditions can include nitrosamines (Ragsdale et al., Inorg. Chem. 4:420 (1965), some of which may be carcinogenic. In addition, NONOates generally release NO, which is rapidly consumed by hemoglobin and can be toxic in individuals with arteriosclerosis. Further, the elasticity of known NO-delivering polymers is generally inadequate, making it difficult to coat medical devices with the polymer and deliver NO with the coated device under physiological conditions. Protein based polymers have a high solubility in blood, which results in short lifetimes. Finally, many NO-delivering polymers cannot be sterilized without loss of NO from the polymer and amounts of NO delivered are limiting.
There is, therefore, a need for new compositions capable of delivering NO to treatment sites in a manner which overcomes the aforementioned shortcomings.
The present invention relates to novel polymers derivatized with NOX, wherein X is one or two. It has now been found that medical devices coated with the novel polymers of the present invention are effective in reducing platelet deposition and restenosis when implanted into animal models. Specifically, stents coated with an S-nitrosylated xcex2-cyclodextrin or an S-nitrosylated xcex2-cyclodextrin complexed with S-nitroso-N-acetyl-D,L-penicillamine or S-nitroso-penicillamine resulted in decreased platelet deposition when inserted into the coronary or cortoid arteries of dogs compared with stents which lacked the polymer coating (Example 12). It has also been found that S-nitrosylated xcex2-cyclodextrin and S-nitrosylated xcex2-cyclodextrin complexed with S-nitroso-N-acetyl-D,L-penicillamine cause vasodilation in bioassays (Examples 8 and 10). Furthermore, compositions comprising S-nitrosylated cyclodextrins complexed with S-nitrosothiols have been found to deliver NO-related activity for extended periods of time and to exhibit increased shelf stability compared with compounds presently used to deliver NO in vivo. Specifically, S-nitrosylated xcex2-cyclodextrin complexed with S-nitroso-N-acetyl-D,L-penisillamine can be stored for at least three weeks without losing NO and to deliver NO in physiological solutions for periods of time greater than 24 hours (Example 10). Lifetimes of many months have been observed (Examples 9 and 10).
The present invention includes novel nitrated or nitrosylated polymers. Thus, the novel polymers are derivatized with NOX. The polymer has at least one NOX group per 1200 atomic mass units (amu) of the polymer, preferably per 600 amu of the polymer, and even more preferably per 70 amu of the polymer. In a preferred embodiment, the polymer has pendant xe2x80x94Sxe2x80x94NO and/or pendant xe2x80x94Oxe2x80x94NO groups, i.e. the polymer is S-nitrosylated and/or O-nitrosylated. In another embodiment, the polymer is prepared by reacting a polythiolated polysaccharide with a nitrosylating agent or a nitrating agent under conditions suitable for nitrosylating or nitrating free thiol groups.
Another embodiment of the present invention is a method of preparing a polymer having NOX groups. The method comprises reacting a polymer having a multiplicity of pendant nucleophilic groups with a nitrosylating agent or a nitrating agent under conditions suitable for nitrosylating or nitrating free nucleophilic groups. In a preferred embodiment, the polymer is a polythiolated polymer.
Another embodiment of the present invention is a method of delivering nitric oxide to a treatment site in an individual or animal. The method comprises providing a medical device coated with a polymer derivatized with NOX, as described above. Preferably, the polymer is an S-nitrosylated polymer. The medical device is then implanted into the individual or animal at the treatment site. For delivering nitric oxide to a bodily fluid, for example blood, the bodily fluid is contacted with the coated medical device.
Yet another embodiment of the present invention is a method of preparing a device for delivering nitric oxide to a treatment site in an individual or animal. The method comprises coating a medical device suitable for contacting the treatment site in the individual or animal with a polymer derivatized with NOX, as described above. Preferably, the polymer is an S-nitrosylated polymer.
Another embodiment of the present invention is a medical devise for delivering nitric oxide to a treatment site in an individual or animal. The device comprises a medical device suitable for implantation at the treatment site in the individual or animal and which is coated with a polymer derivatized with NOX, as described above. Preferably, the polymer is an S-nitrosylated polymer.
Another embodiment of the present invention is a method for replacing a loss of NO groups from an S-nitrosylated polymer. The method comprises contacting the S-nitrosylated polymer with an effective amount of a gaseous nitrosylating agent such as nitrosyl chloride (NOCl) under conditions suitable for nitrosylating free thiols.
S-nitrosylated cyclodextrins of the present invention undergo heterolytic cleavage of the xe2x80x94Sxe2x80x94NO group, and consequently do not principly release NO. These polymers have a high NO capacity and incorporation of nitrosylating agents such as S-nitroso-N-acetyl-D,L-penicillamine into the polymer matrix increases the stability of S-nitrosylated cyclodextrins to weeks or more. The incorporation of nitrosylating agents also increases their capacity to deliver NO by about two fold over native cyclodextrin and by about two hundred fold over protein based polymers. The combination of increased stability and capacity to deliver NO results in a high NO potency, a controlled delivery of NO and extended treatment and storage lives for the polymer. A further advantage of these polymers is that they lack the brittleness of other NO-delivering compositions and have sufficient elasticity to coat and adhere under physiological conditions to medical devices such as stents.